And those powerhouses are much more complex than the old controllers. For example to actually save power it is no longer enough to reduce the clock speed, but power gating has to be taken into account. A timer no longer has two registers but 16, etc.
It is much easier to solve such things once and then reuse, ergo have an OS based setup, instead of trying to think of all those things all the time.
Also, If you haven’t done that already, @RTOS1 I would advise you to look into the actual code(size) of FreeRTOS in particular. A lot of the concepts solved there will be necessary for a “can be solved bare metal” application anyway, while I wouldn’t bet on that “bare metal solution” to actually be much smaller.
It is a completely different category from what Linux, or even Zephyr, does.